The speed and bandwidth of data transmission over fiber optic cable renders optical fiber communication particularly advantageous for certain applications. In order to build and implement the requisite optical fiber infrastructure, there is a need for fiber optic connectors. Fiber optic connector systems typically comprise mating ferrules held by respective housings. The ferrules retain fibers in a fixed position within a fiber passage. The fiber held by the ferrule is polished to a flat mirror finish. An endface of the fiber is finished to be flush with an endface of the ferrule. Two polished fibers mate in coaxial alignment to effect an interconnection. Any irregularities, burrs or scratches in the fiber finish disperse or reflect light at the interconnection adversely affecting light transmission. In singlemode connectors, a ferrule endface having an endface transverse to the ferrule axis permits back reflections to propagate back towards the source of the light. To reduce the power of back reflections, there is known a ferrule having an angled endface ("APC" ferrule). The APC ferrule geometry advantageously diverts back reflections into the cladding of the fiber. In known APC ferrule endface geometry, the endfaces are arranged to mate in abutting contact with the endface surfaces parallel to each other.
A central portion or core of the fiber actually carries the optically encoded information. Optically encoded information traveling along the fiber optic core held in one ferrule and is received by the fiber core in the mating ferrule. Perfect concentricity of fiber cores permits maximum light transmission over the interconnection. Eccentricity of mating fiber cores increases insertion loss. A condition of gross misalignment can prevent transmission altogether. It is, therefore, important that fiber cores mate in coaxial alignment.
A fiber optic connector requires mutual alignment of respective fiber cores in a repeatable separable interconnect. The connector must also maintain performance characteristics over multiple matings and unmatings under various environmental conditions. A separable fiber optic interconnect introduces the possibility that dust may accumulate on the endface of the fiber core that may disperse and/or inhibit transmission of the light beam. Larger fiber cores are relatively resistant to the adverse affects of dust. Transmission performance of smaller fiber cores, such as singlemode fiber having a fiber core diameter of 9 microns, with a single spec of dust, however, is unacceptable. Environmental conditions, such as heat and vibration, may adversely effect concentricity of fiber optic cores over time causing unacceptable gaps in transmission. There is a need, therefore, for a robust fiber optic connector and for a fiber optic connector that is more resistant to fiber core misalignment.
There is known, an expanded beam connector system comprising first and second ferrules, each housing a fiber. A first discrete lens is mounted adjacent an endface of the first ferrule. The first lens receives a light beam from the first ferrule and expands the beam to a relatively larger diameter. The second ferrule and lens is similarly configured. The second lens of the mating connector receives the expanded beam and refocuses it to a fiber held in the second ferrule. The separable interface is in the plane of the mating expanded beams. The intersection of mating expanded beams defines a beam coupling region. An expanded beam connector system is robust by virtue of the larger beam coupling region rendering it more resistant to dust and misalignment. The lenses being discrete, however, create a bulky package in contravention of the desire to miniaturize connectors.
A fiber optic array connector system known as the MT style connector interconnects a plurality of fibers in two mating connectors. The MT style connector includes a multiple fiber ferrule, or array ferrule. Terminated and polished array ferrules mate in abutting relation similar to single fiber ferrule connectors. The endface finishing of a terminated array ferrule, is however, more difficult than a single fiber ferrule. The enhanced difficulty is due to the requirement for endface uniformity along all fibers. The enhanced difficulty is exacerbated when polishing an angle on a fiber array ferrule. Known APC fiber array ferrules require a finished flatness of less than 0.1 micron and angle uniformity of less than 0.1.degree. over all fibers in order to yield an acceptable part. Nonuniformity in the finish of the endfaces causes gaps between some mating endfaces which increases insertion loss and back reflection between some, but not all, of the mating fibers. If all fibers do not have an acceptable endface finish, the entire fiber array ferrule is unacceptable. A known solution uses index matching gel between mating ferrules. The index matching gel is an acceptable solution for a fixed interconnect such as a splice, but is inappropriate at a separable interconnect. There is a need, therefore, for a multiple fiber ferrule having acceptable insertion loss under less stringent endface finish specifications.
For APC fiber array connectors, obtaining a finished angled endface on a fiber optic array ferrule is possible, but substantially more challenging than obtaining an angled endface on a single fiber ferrule. An APC MT connector requires use of a precision polishing process on the highest grade parts performed by skilled individuals. The precision polishing process is time consuming and, therefore, more costly to perform. Current technology requiring precision polishing on the highest grade ferrule produces APC array ferrules with relatively low yields rendering acceptable ferrules more costly. There is a need, therefore, for an APC array ferrule that is more resistant to endface finish irregularities.